The chances of pinning this down to one person or era is. . . . . none. These things tend to develop incrementally, sometimes an off shoot from something else, often developing in separate locations but within the same time frame. We have trouble determining who invented the light bulb or the transistor and they were both relatively recent. Determining who got to the patent office first is pretty easy though.

The academic paper by Prof. Julio Ribeiro Alves that I cited twice in this thread is rather thorough. It presents various theories on the early origins and reviews a number of points in the literature. There is consideration of the lute and the differences with the guitar. The paper then analyzes the question beginning with the vihuela and 4 course guitar. Finally, it considers the 5 and 6 course guitar. It is worth the time spent reading it, IMO.

The academic paper by Prof. Julio Ribeiro Alves that I cited twice in this thread is rather thorough. It presents various theories on the early origins and reviews a number of points in the literature. There is consideration of the lute and the differences with the guitar. The paper then analyzes the question beginning with the vihuela and 4 course guitar. Finally, it considers the 5 and 6 course guitar. It is worth the time spent reading it, IMO.

The underlying question seems to be, "What culture gets credit for the creation of the guitar?"

Just as with border lines between countries, distinctions between cultures are artificial. Cultures interact like oil paint on a canvas: they blend together, sometimes forming new colors, other times interlacing and intertwining but retaining some degree of their own identity.

And how do we define a guitar? Different people are going to have different definitions, and each definition is going to have its own history (or, more accurately, set of histories). Even attempting to define "guitar" is problematic. Consider this: A classical guitar and an oud have much more in common than a classical guitar and an electric guitar.

There's also an implicit assumption that there must be a singular birthplace, but what we think of as "the guitar" isn't really a singular entity. It's actually a category word: the term "guitar" is a catch-all phrase that encompasses thousands of varying designs spanning thousands of incredible instrument makers.

So imagine every stringed instrument maker that ever existed in the history of humanity. Now narrow that down to the ones that had a new idea (even a small one) and executed that idea in one of their instruments. What were their birthplaces? If we could know that, we would have an answer to your question.

The underlying question seems to be, "What culture gets credit for the creation of the guitar?"

Just as with border lines between countries, distinctions between cultures are artificial. Cultures interact like oil paint on a canvas: they blend together, sometimes forming new colors, other times interlacing and intertwining but retaining some degree of their own identity.

And how do we define a guitar? Different people are going to have different definitions, and each definition is going to have its own history (or, more accurately, set of histories). Even attempting to define "guitar" is problematic. Consider this: A classical guitar and an oud have much more in common than a classical guitar and an electric guitar.

There's also an implicit assumption that there must be a singular birthplace, but what we think of as "the guitar" isn't really a singular entity. It's actually a category word: the term "guitar" is a catch-all phrase that encompasses thousands of varying designs spanning thousands of incredible instrument makers.

So imagine every stringed instrument maker that ever existed in the history of humanity. Now narrow that down to the ones that had a new idea (even a small one) and executed that idea in one of their instruments. What were their birthplaces? If we could know that, we would have an answer to your question.

Good points! As you say, borders have changed numerous times since the guitar was born. It would be a better clue to have a closer look at the cultures maybe. But it is also true that the history of the guitar (Just like the history itself) has different versions. In this case, maybe there is not enough evidence to prove which one is the one but some versions are more valid than the others.

To send light into the darkness of men's heart, such is the duty of the artist. (Robert Schumann)

When looking at Persian instruments, similar names like Tar, Dotar and Setar are very similar to Guitar and their construction is not far from guitar. Also Lute that has been assumed as a guitar ancestor come from the Arabian word Al-ud.

When I consider some of the historical facts (at least in most versions) and look at it from a cultural aspect, it leads me to believe that the guitar has been a middle eastern instrument and has been gradually changed and to the shape and form we know it today.

Let's not forget the fact that classical guitar is still changing... unlike violins and cello for instance...

To send light into the darkness of men's heart, such is the duty of the artist. (Robert Schumann)

The deep roots of the guitar may have been the kithara of classical Greece. Note the similarity in the sound of names for the two instruments: kithara and guitar. That is just one theory.

The Classical Greeks used both their lyre and kithara to accompany choral music, singing and song. The players performed music written in unison rather than in part harmony. The CGs had and/or used no harmony per se. Perhaps that was because they held a high value for the voice, for training the voice, and for the interval of the unison: the most perfect interval.

Looking at this thread, the more basic problem is how is the guitar defined. If we are talking about the 6th string guitar, which involved out of the Baroque guitar, the time period would seem to point to the 1770s, and somewhere between Paris, Napolis, and Vienna. If we are talking about guitar shaped instruments with frets, the answer would point to very ancient sources-- (which probably are not directly related to the modern 6th string guitar).

Looking at this thread, the more basic problem is how is the guitar defined.

I think this is the crucial point. As far as I understand there is no precise definition of a "guitar" that allows to judge whether an instrument is a guitar or not. It's the same with computers. No-one knows the birth place of a computer because there is no common agreement what belongs to a computer and whether a machine is a computer or not.

But we could chose a different approach. We could simply say that a "guitar" is a guitar, that means that every musical instrument that was named "guitar" in the past is a guitar, and all other instruments aren't guitars even if they look like a guitar. If we take this approach then the birth place of the guitar would be (the ancient) Greece.

Happiness is when what you think what you say and what you do are in harmony.

But we could chose a different approach. We could simply say that a "guitar" is a guitar, that means that every musical instrument that was named "guitar" in the past is a guitar, and all other instruments aren't guitars even if they look like a guitar. If we take this approach then the birth place of the guitar would be (the ancient) Greece.

Could you clarify this? The Ancient Greek instrument was called 'kithara'. That may be the derivation of the word 'guitar' but are you saying it is the same word? If so, what about 'cittern', 'gittern' or 'guittar' (aka 'citra')? And what about other languages; many of the words are quite similar: guitarra, gitaar, kitaar, kitarë, gitaar, ghytar, gitarra, gitarre, but occasionally somewhat different: 'jita' (Chinese), and occasionally very different: 'isiginci' (Zulu). On the other hand the fairly similar word 'zither' describes what is surely a different instrument. So how do you decide which words are describing instruments that you accept as guitars?

Could you clarify this? The Ancient Greek instrument was called 'kithara'.

Ok, I'm no linguistic expert. To my understanding the word κιθάρα (Kithara) was the origin of the word guitarra or guitar, and the other similar words in the Arab world or later on in north Africa were derived from that, but I might be wrong of course. In the (German) Wiki I find the same information about the history of a guitar. Sometimes words sound similar but have different origins, so I can't say for sure if for example the Chinese word jita has anything to do with the ancient Greek word kithara.
EDIT: I want to add that I simply wanted to describe a different approach how the question of the OP can be answered, I don't want to say that this is the right way to define the term guitar.

Happiness is when what you think what you say and what you do are in harmony.

But we could chose a different approach. We could simply say that a "guitar" is a guitar, that means that every musical instrument that was named "guitar" in the past is a guitar, and all other instruments aren't guitars even if they look like a guitar. If we take this approach then the birth place of the guitar would be (the ancient) Greece.

Could you clarify this? The Ancient Greek instrument was called 'kithara'. That may be the derivation of the word 'guitar' but are you saying it is the same word? If so, what about 'cittern', 'gittern' or 'guittar' (aka 'citra')? And what about other languages; many of the words are quite similar: guitarra, gitaar, kitaar, kitarë, gitaar, ghytar, gitarra, gitarre, but occasionally somewhat different: 'jita' (Chinese), and occasionally very different: 'isiginci' (Zulu). On the other hand the fairly similar word 'zither' describes what is surely a different instrument. So how do you decide which words are describing instruments that you accept as guitars?

The Chitarra Italiana (Italian: [kiˈtarra itaˈljaːna]; 'Italian guitar') is a lute-shaped plucked instrument with 4 or 5 single and sometimes double strings, in a tuning similar to that of the guitar [modern]. The Chitarra was common in Italy during the Renaissance Era [1400 through 1600 CE]. According to Renato Meucci, the designation of 'Italiana' followed the introduction to Italy of the flat-backed development of the instrument, referred to as chitarra alla spagnola: literally 'Spanish guitar'; to distinguish between the two versions. It is believed to have descended from Panduras, the Mediterranean lutes of Antiquity, and to be related to north African Quitra (or Kitra).

Its bass variety was known as Chitarrone. Musicologist Laurence Wright wrote about the chitarrone in a letter to the Early Music journal (October 1976), "The chitarrone implied "large guitar", that it had a rounded back and was likely do be taken for a smaller lute, and that it was found from the 13th C to the 18th C, but was much more rare in the latter centuries." Additionally, Wright wrote, "In latter years, when the mandola was popular, the chitarrone was at times confused with the mandola."